Diseases caused by retroviruses are becoming alarmingly prevalent. Sexually transmitted retroviral infections and those transmitted by blood transfusion have been the focus of intensive research efforts over the past several years. The tools of modern molecular biology have yielded many of the secrets of retroviral infection, maturation and replication. The present invention concerns the discovery that certain short peptides are useful in treating retroviral infections because the peptides can inhibit the action of the retroviral proteases. The invention also relates to methods for discovering other compounds which display retroviral protease inhibitory activity.